OS X Yosemite public beta signup
apple.com
apple.com
This is still a beta and should be treated as such. I know I had major issues with the last OSX beta I put on mine.
I've usually heard the betas of OSX have been quite stable. Considering they are going to run a public beta of this I would assume it's more stable than usual OS betas they released. I was considering installing it on my main system (I only have one Mac) but you've put me off a bit. What happened to your system?
[0] https://developer.apple.com/devcenter/ios/index.action
Edit: This is only for people who are members of the Developer Program. I only pay for iOS and I have access to OS X too so you probably only need membership from the one of the developer programs.